Thixotropic compositions



Patented Sept. 16, 1952 THIXOTROPIC COMPOSITIONS Birger W. Nordlander, Schenectady, N. Y., as-

signer to General Electric .Qompany, a corpora.-

tion of New York No Drawing. App n mb r 3.1.,..1B9. Serial 136,415

(CLv 260-40) '15 Claims.

This invention relates to thixotropic compositions, and more particularly to polymerizable thixotropic coating and filling compositions comprising a polymerizable liquid and a filler.

A problem of long standing encountered in factory practice in connection with the use of conventional varnishes for coating or filling applications is the excessive drainage from the coated or filled part after the varnish has been applied. A portion of this drainage occurs at .room' temperature immediately after the part has been removed from the treating tank because .of ,the' fluid nature of the conventional varnishes generally employed. This drainage continues until sufficient solvent has evaporated to cause the viscosity of the varnish on the surface or in the interstices of the treated object to become sufiiciently high to enable it to remain in position. It is obvious that the nature of the process is such that too much of the varnish drains away from the top of the treated part and a surplus collects at the bottom of the part, resulting in avery uneven and undesirable ultimate distribution of the varnish base throughout the part. Further drainage occurs duringthe early stages of any baking process which might be involved, when the varnish base remaining in the treated part becomes increasingly fluid as the temperature is increased. This drainage will continue until the temperature. is suiilciently high, and has been applied sufficiently long to cause the varnish-to thicken or skin over due to polymerization reactions of one type or another, such as condensation, oxidation and addition reactions. Conventional varnishes also have a disadvantage in that they draw away from sharp corners and edges, leavin-g'these regions practically bare;

The net result of methods of coating and filling in such a manner is very uneconomical utilization of the weight of varnish originally applied, only a fraction oeing retained. Furthermore, an undesirablyuneven distribution of the varnish in the interstices and on the surface of thetreated part results. i

Where the problem of coating or filling elec- "trical devices, such as, for example, electrical coils, has been involved, the amount of material retained after a single application "is in most cases insufiicient to afford a structure "having the required electrical and .mechanical plete filling becomes impossiblenemploy 'ri the coating and filling compositions heretofore known in the art, not only because of the fact that the inert, volatile solvent in the composition must be expelled after each application, but also because many voids are sealed off during the evaporation of the solvents, In many cases these voids cannot be filled by additional-varnish regardless of how many subsequent treatments are, applied to the structure. This causes the treated structure to have an unequal thermal conductivity from one part to another as well as a much lower over-all heat dissipation rate as compared with a completely void-free structure. In high voltage equipment the presence of voids in the insulation also gives rise to internal corona discharge with resulting deterioration of the insulation. 1

Certain of the above difiiculties can be eliminated by the use of so-called solventless varnishes. This term is intended in the present disclosure to cover compositions of matter which are polymerizable fluids substantially free of inert, volatile solvents such as those used in conventional'varnishes, and which, by the incorporation of suitable catalysts, may be caused to polymerize to form substantially infusible and insoluble materials without the necessity of taking up oxygen from the air and without forming volatile products.

,Since the conversion from the fluid to th hard, infusible stage occurs with little or no also to maintain this condition subsequently during the curing operation, provided that substantially no drainage of varnish occurs during the'baking process.

, Many of the solventless varnishes of the type with which the present invention is concerned, and which will be hereinafter more fully described, comprise fairly fluid, non-volatile compositions. Therefore, in comparison with the conventional varnishes containing highly viscous or solid bases, these solventless varnish compositions suffer the'disadvantage that they do not become increasingly viscous on-standing at room temperature by the evaporationof a volatile inert solvent. As a resultan open structure coatedor filled with such asolventless varnish composition will continuously suffer loss of the varnish by drainage after it has been withdrawn from the treating tank gand'before it has been polymerized by heating. Furthermore, incommon with the conventional varnishes containing appreciable amounts of solvents, many of the solventless varnishes have the disadvantage that during the early stages of the curing process their viscosity is substantially reduced, further aggravating the drainage problem. The difficulties arising out of this property of, the solventless varnishes in many cases have proved to be serious enough to ofiset the principal advantage in using the solventless varnishes for the filling of open structures.

It is an object of the present invention to pro.- vide liquid coating and filling compositions which will not drain from objects prior to and during curing. 7

Another object of this invention is to provide coating and filling compositions which may be applied and cured without loss of the composition.

A further object of the present invention is to provide coating and filling compositions which when applied to objects will remain in situ before and during curing even in corners and sharp edges.

It has been discovered that the advantages in the use of solventless varnishes may be realized in coating and filling operations and at the same I time the disadvantage of excessive drainage may be avoided by employing the compositions of this invention. These compositions may be converted by meansof heat to an infusible and insoluble state and are suitable in general for coating and filling operations and particularly for the insulation of electrical equipment. After a coating of one of the present compositions has been applied to a part, little or no drainage of the composition from the part occurs, either at room temperature or at the elevated temperatures required for complete conversion of the composition to'the infusible and insoluble state. The unusual combination of properties characterizin these compositions rests in the discovery that suitable quantities of I certain specific fillers in combination with solventless varnishes or polymerizable liquids, form compositions which are fluid as long as they are kept in an agitated condition but solidify shortly of fillers'into a varnish will reduce the fiow of the resulting mixture by reason of increased viscosity, this general property is not relied upon for the properties of the present compositions. The specific fillers which are here employed with solventless varnishes form thixotropic compositions capable of undergoing isothermal, reversible, sol-gel transformations, a fluid sol condition existing as long as the mixture is agitated, the sol reverting to a gel within a very short time after agitation has ceased. However, upon heating the gel it polymerizes into an infusible product which is no longer capable of reversion to the fluid sol state. The system may be simplyexpressed by the following relationship:

At rest Heat Fluid sol :2 gel-like solid polymerized product Upon agitation The term thixotropy is used herein to denote the property of a fluid filler-liquid composition to revert rapidly on standing into a gel-like mass having sufiicient cohesive strength to withstand distortion by gravitational force when suspended. freely as in an inverted receptacle or on a coated 4 object. The gel is also of such a nature that it can be fiuidified by the application of mechanical agitation as by shaking, stirring, vibrating, etc. The property of thixotropy as understood herein is thus characterized by a reversible isothermal 501 S gel transition.

The compositions referred to above as solventless varnishes which are employed in combination with specific fillers to form the thixotropic composition of this invention are polymerizable fiuids comprising an unsaturated alkyd resin. These liquid unsaturated alkyd resins are the reaction products of polyhydric alcohols, mixtures of polyhydric alcohols or mixtures of polyhydric and monohydric alcohols, and an alpha unsaturated alpha,b'eta' polycarboxylic acid or a plurality of polycarboxylic acids, one of which, at least, is an alpha unsaturated alpha,beta polycarboxylic acid, the resinous material having an acid value of up to 60 and preferably between 45and 60. Examples of such polyhydric alcohols are ethylene glycol, diand triethylene glycols, propylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene gylcol, glycerine or pentaerythritol in in combination with a monohydric alcohol, etc. Examples of unsaturated polycarboxylic acids are maleic, fumaric, and itaconic acids Anhydrides of polycarboxylic acids may also be employed. The term polycarboxylic acid as used herein is intended to include within its meaning theanhydrides of such acids. .In addition to one or more of the unsaturated polycarboxylic acids, saturated polycarboxylic acids may also be present in the reaction mixture in the preparation of the resins referred to above. Examples of such saturated polycarboxylic acids are succinic, adipic, sebacic and phthalic acids.

In addition to the above unsaturated alkyd resins, the polymerizable fluids which'areluse'd in the present compositions may contain'polymerizable substances such as, for example, esters of unsaturated monohydric alcohols and polycarboxylic acids, including unsaturated polycarboxylic acids, halogenated aromatic polycarboxylic acids and polybasic inorganic acids. Examplesof such substances are diallyl phthalate, diallyl succinate, diallyl maleate, diallyl fumarate, diallyl itaconate, diallyl ohlorophthalates and triallyl phosphate. Othersubstances which may be incorporated in these polymerizable liquids are esters of monohydric alcohols and unsaturated polycarboxylic acids which are capable of coabout 150 C., or more preferably from about C. to about C. However, for practical reasons, it is desirable to incorporate a polymerization catalyst in order to accelerate the polymerization of the coating or filling compositions. Any of the catalysts known to those skilled in the art may be employed. Examples of such catalysts which have been found to be particularly suitable are benzoyl peroxide, tertiary butyl perbenzoate, ditertiary butyl diperphthalate, and tertiary butyl hydroperoxide. Any suitable'amount of catalyst may be used, but in general the "catailyst-concentration will be within the range of from about 0.5 to about 2.0 percent byweight of the polymerizable liquid.

-.- Ineopendin applications-finial Nos, ream, -;136;4;1'3, 1.353.112, 71363216,, 13 M117, and iii fiiilfi, rfiled concurrentlyherewith and ashamed to the same .assignee as the present invention, there haye vbeen :desoribed rertain'other .thiiiotrop '1 solventless varnish zcompod tions. 101. been round that powdered, dehydrated silica zaero which consists essentiauy of silica :aemeel has very useful properties :in conjunction with the tnroduction of tinxotropic .solventlessi-varmsh:mawterlals.

All parts .ghien :in the enemies by we ght.

Example ;1

.. 4,5 Tertiary butyl perbenzoatemmr-.-.-.,.m...i-+ a f. 59 fiilica aero'gel (powdered) ,i-,.M ..,.-m-i 1191) :The above "materials y e d d :a smooth, highly jthixotropic mixture otter thorough stirring, .A

glass rod when dipped in the composition and -.sus nended atroom temp rature, shew-edno dra nage after sixteen hours. -Neither W545 zany-drainage apparent after sixteen more hoursat .1003 C. during which period cure was effected. This is in direct contradisti-nction to results obtained with the above composition when no filler was used at-all or whenanon-efiecti-ve filler was used such as flint or ,muscovite mica. ,In both the above cases only a very small fraction of the original coating remained after the rod was dipped in the material and allowed to hang ior .-.sixte.en hours at room temperature :and was r .oured ror sixteen hours at .100 Example 2' l *iParts 'Dia'll-yl phthala'teum;..; .....,.,.-..a. e,... ,4411 l'i'Diethylene glycol-maleate ,.-.j i r441) Tertiary but-yl perbenzoate 1.0 Silicaaemgel (powder-ed) V "11.0

.The above ing edients iormed :a sm oth hlend having pronounced thixoltr-opic characteristics when ,mixed by stirring. Atglass rod dihped in :the composition and withdrawn showed no drainage of .rnaterial (after sixteen hours at room temperature. .Eur her treatment at 190 :0. for-sixteen hours also resulted in no dra n ge. Wh neured, these materials ar characterized by extrem tou hnessr o r i The 'thixotropy-producing ualities of the silica aer gelare so .pronoun ed that when he p rcent by we ht propor ion of vsilica aero el, ,based on 1theweightof the polymerizable ingredient-s, is

above ten to eleven per cent the compositions l produced are too viscous even in their liquefied condition to he of practical use :as aidipping medi run for parts which are to be coated. While the above ocompositi nsare entirely suitable in and of themselves itisoitendesirable that 'thixotropio varni hes su h as herein. described should ,ihave as large an amount of filler as possible. Among the reasons ,for having such lar er amounts of filler are the lowering of shrinkage during polymerization. lowering of costs, roduc- I I tion of temperature noemcient of expansion and increasing the heat conductivity :of the cured product and reducing the exoth rmic natureof th polymerization.

It has been iound that thepresent silica e with its pronounced thixotrony p oducing char- ;a teristi.cs may be used to great aduantage -i-n .eombination with non -!thix tropic roducing fillers to produce OVer-aIl-QOmPQSiELQIw"W iQh i thixotmhic in nature; f

I am V iiDiaillyl pht'halate,.. .r. aaui.i-aa;ma.ai-eaa aa119,25 Dieithylene glycol omaleatemg.

The above mixture was thoroughly mixed to a smooth homogeneous mass which was not thiamtropic in nature. When a 'glasszro'd was dipp d in "thee-mixture and withdrawn fifty-two per cent or'the-materiailhad drained off aiterthangingijor *sixteen hours at :room temperature.

rdmmple 4 Diallyl 'phthalate ,,.m ,,M.,,. 19.5 f lliethylene glycol ma'1eate 19.5 ifliertiary butyl perbenzoate. -i4) .L'Elint (powdered);"panama, ,-i?i9 ;0 J'Silica aerogel '(powdered') 13) Upon thorough mixing, the above ingredients exhibited no thixotropic prope ties Ai-ter produced a smooth, ,homo geneous mass ha ing pronounced thixotropic characteristics. *VVin-no a a glass :rodwasdi pped in the above composition,

withdrawn and hung at room temperature for sixteen hours, there was no 'visible draina e of material from the rod. Neither wasany; drainage apparent after curing for sixteen 1 1oursat'100 C.

It is apparent from this example that as little as 2.56 percent, by weight, of the silica aerogel, based on the weight tofozthe polymerizable ingredients, are effective in inducing thixotropy in -non-th xotropic.oonipositions.

When mixed, .a composition such aaszthat'fahou teen hours :at :room temperature over seventeeight percent of thematerial had drained off from a glass rod which had been dipped in the mixture and withdrawn. 4' t limritplerfi 7 "Pants Diallill :nhthalateMigraine"and" a- .2110 Diethylene glycol maleate, m 21.0 Tertiary ibutyl "pe. .benzoate 11,0 Flint 1(-powdered) H1550 vA composition:eontainingthe aboveiingredients, .mixedfby thorough stirring-exhibited pronounced ,thixotropy. There was :no apparent .drai-nage from a g1ass:r0d, dip-coated-with theicomposition, after sixteen hours at room ,,temperature or sixteen hours additional at"'100- C.

. D ama .7

mania. natnaiaiannnm hwamv a. an Diethylene glycol maleateumadwwma,;. 2425 ertiary butyi perhenzoate"Mud"..-P,ino :150

' Flint (powdered) v 50.0

when aglasarod-was dipwoatedwith-the-com- 1 951141 11 hreparedhy thoroughly mixing the above z,;i -rigredients about eighty-pix ercent of the coati material had drained off after the rod had hung in air at room temperature fromisiiite'en hours.- The torrimoi-hon.v exhibited morthixotrc ic JP -Qm ties.

-thixotropic composition upon stirring.

and none after 7 Example-8 Parts Diallyl phthalatefl 23.25 Diethylene glycol maleate 23.25 Tertiary butyl perbenzoate; 1.0

Flint (powdered) 50.0 Silica aerogel (powdered) 2.5

Pronounced thixotropic properties were apparent when the above ingredients were mixed by stirring into a smooth homogeneous mass.

.When a glass rod .was dip-coated with the material, there was no apparent drainage of the material from the suspended rod after sixteen hours at room temperature or after an additional sixteen hours at 100 c.

Example 9 a Parts Diallyl phthalate 30.3 Diethylene glycol maleate 30.3 Tertiary butyl perbenzoate 1.0 Muscovite mica (powdered) 39.4

When the above ingredients were thoroughly mixed together, no thixotropic properties were apparent. When a glass rod dip-coated with the composition was suspended at room temperature for sixteen hours the drainage loss of material was about thirty-three percent. After sixteen hours at 100 C., about nineteen percent more of the material had drained on.

Example 10 Parts Diallyl phthalate 30.3 Diethylene glycol maleate 30.3 Tertiary butyl perbenzoate 1.0 Muscovite mica (powdered) 36.9 .Silica aerogel (powdered) 2.5

The smooth composition obtained by mixing together the above ingredients exhibited pronounced thixotropic properties. There was no drainage from a glass rod dipped in the composition after hanging sixteen hours at room temperature and sixteen hours at 100 C.

Emample 11 Parts Diallyl phthalate 32.5 Diethylene glycol maleate 32.5 Tertiary butyl perbenzoate 1.0 Muscovite mica (powdered) 35.0

Example 12 Parts Diallyl phthalateuu; 32.5 Diethylene glycol maleate 32.5 Tertiary butyl perbenzoate 1.0 Muscovite mica (powdered) 32.6 Silica aerogel (powdered) 2.4

The above ingredients produced a smooth, A glass rod dip-coated with the material showed no drainage after sixteen hours at room temperature an additional sixteen hours at From the above examples it will be apparent that not only will the silica aerogel of the'present' tungsten oxide and nickel oxide.

invention produce desirable thixotropic materials in conjunction with the solventless' varnishes described herein, but that when' incorporated in relatively small amounts it will cause such varnishes containing fillers which are non-effective in this respect to become thixotropic.

'Solventless varnish compositions containing non-efiective fillers, other than those given in the above examples, may also be rendered thixotropic by means of small added amounts of the present silica gel. Among such inert fillers are silex or sand, talc, Carborundum, Alundum, litharge, iron powder, zirconium oxide, calcium tungstate, This ofiers a convenient method of controlling the thixotropic characteristics of the present compositions while retaining a high total filler content and utilizing to advantage whatever outstanding physical property (dielectric, moisture resistance, hardness, tensile strength, toughness, etc.) that the inert filler may contribute to the final heathardened product.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A 'thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation oi. a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and a filler comprising silica aerogel, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight of the polymerizable fluid.

2. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta. polycarboxylic acidand a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a filler comprising silica aerogel, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight 01 the polymerizable fluid. I

3. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and an ester of monohydric alcohol and an unsaturated polycarboxylic acid capable of copolymerizing with unsaturated alkyd resins and a flller comprising silica aerogel, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight of the polymerizable fluid.

4. A thixotropic composition comprising a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation of a mixture of ingredients comprising diethylene glycol and maleic anhydride and diallyl phthalate and a filler material comprising silica aerogel, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight of the polymerizable fluid.

5. A thixotropic composition com rising. a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation of a mixture of ingredients comprising diethylene.

glycol and maleic anhydride and a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a flller comprising silica aerogel, the silica aerogel comprising from 2.55 to 11 percent, by weight, based on the weight of the polymerizable fluid. j

6. A thixotropic composition comprising a 9 polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and a filler comprising silica aerogel and flint, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight of the polymerizable fluid.

7 A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a flller comprising silica aerogel and flint, the silica aerogel comprising from 2.56 to 11 percent, by weight, based on the weight of the polymerizable fluid.

8. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha,beta polycarboxylic acid and an ester of a monohydric alcohol and an unsaturated polycarboxylic acid capable of copolymerizing with unsaturated alkyd resins and a flller comprising silica aerogel and flint, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

9. A thixotrop-ic composition comprising a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation of a mixture of ingredients comprising diethylene glycol and maleic anhydride and diallyl phthalate and a filler material comprising silica aerogel and flint, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

10. A thixotropic composition comprising a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation of a mixture of ingredients comprising diethylene glycol and maleic anhydride and a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a filler comprising silica aerogel and flint, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

11. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and a flller comprising silica aerogel and Muscovite mica, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

12. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated alpha,beta polycarboxylic acid and a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a filler comprising silica aerogel and Muscovite mica, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

13. A thixotropic composition comprising a polymerizable fluid comprising a liquid unsaturated alkyd resin obtained by the esteriflcation of a mixture of ingredients comprising a polyhydric alcohol and an alpha unsaturated al ha,beta polycarboxylic acid and an ester of a monohydric alcohol and an unsaturated polycarboxylic acid capable of copolymerizing with unsaturated alkyd resins and a flller comprising silica aerogel and Muscovite mica, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

14. A thixotropic composition comprising a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation of a mixture of ingredients comprising diethylene glycol and maleic anhydride and diallyl phthalate and a filler material comprising silica aerogel and Muscovite mica, the silica aerogel comprising, by weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid. V 1

15. A thixotropic composition comprising a polymerizable fluid comprising liquid diethylene glycol maleate obtained by the esteriflcation 01 a mixture of ingredients comprising diethylene glycol and maleic anhydride and a polymerizable ester of an unsaturated monohydric alcohol and a polycarboxylic acid and a filler comprisingsilica aerogel and Muscovite mica, the silica aerogel comprising, by Weight, from 2.56 to 11 percent, based on the weight of the polymerizable fluid.

BIRGER W. NORDLANDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,416,620 Gans et a1 Feb. 25, 1947 2,443,736 Kropa June 22, 1948 2,482,086 Foster Sept. 20, 1949 OTHER REFERENCES Industrial Chemistry of Colloidal and Amorphous Materials by Lewis et al., published in 1943 by MacMillan Co., page 327. 

1. A THIXOTROPIC COMPOSITION COMPRISING A POLYMERIZABLE FLUID COMPRISING A LIQUID UNSATURATED ALKYD RESIN OBTAINED BY THE ESTERIFICATION OF A MIXTURE OF INGREDIENTS COMPRISING A POLYHYDRIC ALCOHOL AND AN ALPHA UNSATURATED ALPHA, BETA POLYCARBOXYLIC ACID AND A FILLER COMPRISING SILICA AEROGEL, THE SILICA ACEROGEL COMPRISING FROM 2.56 TO 11 PERCENT, BY WEIGHT, BASED ON THE WEIGHT OF THE POLYMERIZABLE FLUID. 